1. Field of the Invention
The present invention relates to a nonaqueous secondary battery of high energy density and high repeating stability usable as power source for electronic appliance, constituent elements of battery, and electrochemical elements.
The invention further relates to a novel secondary battery of large size, small size, thin type, and light weight usable in the fields of electronic appliance, electric vehicles and others, and more particularly to a lithium ion secondary battery of high energy density of which current collector is composed of a flexible graphite sheet.
2. Description of the Prior Art
Along with the enhancement of performance of electronic appliances, the appliances are required to be smaller in size and portable. As a result, secondary batteries of small size and large capacity are demanded. On the other hand, for use as power source for electric vehicle, secondary batteries of large size, light weight, and large capacity are demanded.
Existing secondary batteries include the lead storage battery and nickel-cadmium battery, among others, but to replace them, lithium secondary batteries of higher energy density are attracting wide attention. In lithium secondary batteries, it was first attempted to use metal lithium as active material, but as charging and discharging were repeated, dendritic metals grow on the electrode surface, and if the growth is excessive, it is known to lead to overheating of the battery.
As one of the methods to prevent this, it has been proposed to use a carbonaceous material for absorbing lithium between layers, instead of metal lithium. When a carbonaceous material is used, lithium dendrite does not grow, and it is effective to prevent overheating of the battery.
However, when graphite is used as carbonaceous material, the upper limit of the capacity is 372 mAh/g. Instead of graphite, by using a material obtained by baking pitch at low temperature of 1000xc2x0 C. or less, it is known that a capacity exceeding 372 mAh/g is obtained.
In this low temperature baking of pitch, however, the potential in charging and discharging fluctuates largely depending on the depth of charging and discharging, and it is hard to handle in control of power source.
This capacity is the electric charge density, and for increase of capacity from the viewpoint of energy density, it is disadvantageous when the flat zone of potential is small.
As other method of suppressing growth of lithium dendrite, it is proposed to solidify or gelate the electrolyte solution between positive and negative electrodes. In the conventional battery, liquid electrolyte was used, and dendrites grew, but by solidifying or gelating, it has been known that the dendrite growth is notably suppressed in the direction of the solid electrolyte.
Moreover, by solidifying or gelating, if metal lithium can be used as active material, the lithium performing oxidation and reduction reaction can be directly used as the electrode, and the upper limit of the capacity restricted when using carbon can be increased, and a large capacity is realized.
In the conventional battery, to prevent leak of electrolyte solution, a rigid container and a seal structure were used, which was hindrance to reduction of weight and thickness. Yet, to seal a container in a shape having notch or the like, an expensive and complicated device was needed. By solidifying or gelating the electrolyte, a simple container or seal structure can be used as compared with the case of using liquid, and the battery can be reduced in thickness and formed in a desired shape. More preferably, flash point and other heat resistant stability tend to be higher than in liquid, and it is expected to be beneficial in the assembling and manufacturing process.
Not only larger capacity, but also longer life of secondary battery is also demanded. In most secondary batteries containing lithium ions in the electrolyte, transition metal oxides such as LiCoO2, LiMn2O4, and V2O5 are used in the positive electrode, but these transition metal oxides change in the volume significantly depending on lithium ions moving in and out. Accordingly, as the battery repeats charging and discharging, the performance as secondary battery deteriorates, and finally failing to charge and discharge sufficiently.
In the condenser, on the other hand, liquid electrolyte was used in the inexpensive electrolytic type, but evaporation of electrolyte was one of the factors of aging deterioration of characteristics. To prevent such aging deterioration, instead of liquid electrolyte, it has been attempted to use manganese dioxide or conductive high polymer. Alternatively, by gelating the electrolyte, evaporation may be suppressed. In the case of the gel, a stronger restoration action of the condenser is expected, as compared with solid electrolyte such as manganese dioxide.
In conventional lithium secondary batteries, as disclosed in Japanese Laid-open Patent No. 62-90863, Japanese Laid-open Patent No. 63-121260, and Japanese Laid-open Patent No. 3-49155, a transition metal compound oxide mainly composed of lithium and cobalt is used in the positive active material, and a carbon material in the negative active material. The positive active material is disposed on a metal current collector of aluminum, stainless steel or the like, and the negative active material on a metal current collector made of copper foil of 10 to 20 xcexcm in thickness that is, an aqueous binder or nonaqueous binder is added to the active material, and is applied and held on one side or both sides of the current collector.
Thus, in the conventional lithium secondary battery, since a metal of large specific gravity is used in the current collector, the energy density per unit weight of the battery is not so high. Besides, such current collector is poor in contact with the active material, and the contact resistance increases, which causes impedance increase and cycle deterioration.
Recently, on the other hand, from the standpoint of environmental problems such as air pollution and global warming, large-sized secondary batteries of large capacity as power source for electric vehicles are being developed intensively. As the power source for electric vehicle, nickel-hydrogen absorbing alloy battery, lead storage battery, and nickel-cadmium battery are being put in practical use.
However, the total weight of the battery is very heavy, about 300 to 500 kg, and the energy density per unit weight is small, and the driving distance per one charge is limited, and development of secondary battery of high energy density per unit weight is urgently needed.
As the nonaqueous secondary battery used in the power source for electronic appliance, a larger capacity for longer time of continuous use, smaller size, and lighter weight is demanded. At the same time, high repeating stability for longer life is required. To satisfy these requirements, the nonaqueous secondary battery of high energy density and high repeating stability is demanded. However, to realize the nonaqueous secondary battery or electrochemical elements satisfying both high energy density and high repeating stability, there were problems as mentioned in the prior art.
The invention is to solve these problems, and it is hence an object thereof to realize constituent elements for manufacturing the nonaqueous secondary battery having high energy density and high repeating stability, and nonaqueous secondary battery and electrochemical elements using them.
It is also an object of the invention to present a lithium ion secondary battery of large capacity, excellent in cycle characteristics by improving the current collector to reduce the battery weight.
It is an object of the invention to realize constituent elements for manufacturing a nonaqueous secondary battery having high energy density and high repeating stability, and a nonaqueous secondary battery and electrochemical elements using them.
It is also an object of the invention to present a lithium ion secondary battery of large capacity, excellent in cycle characteristics by improving the current collector to reduce the battery weight.
To solve the problems, the invention relates to a nonaqueous secondary battery having a positive electrode and a negative electrode for absorbing and releasing lithium ions, using an ion conductor containing lithium ions as electrolyte, in which at least one of the positive electrode and negative electrode is made of an active material of which crystal lattice structure and row structure of lithium ions inserted therein are in mismatched relation, and therefore a nonaqueous secondary battery having high energy density and high repeating stability is realized.
In the invention, to solve the problems, the active material is composed of an oxide containing vanadium, and by using it, a nonaqueous secondary battery having high energy density and high repeating stability is realized.
Further, as a result of intensive studies to solve the problems, it is discovered that the porous structure of carbon has a serious effect on absorption of lithium, which has finally led to the present invention. That is, the invention presents the carbon material having the following features and its manufacturing method.
(1) An aromatic compound of 2 to 10 rings is added to the high polymer before curing, and the cured resin is heated.
(2) An aromatic compound of 2 to 10 rings is added to the high polymer before curing, and the cured resin is heated after reaction of aromatic compound and high polymer.
(3) In the cured resin, heat treatment consists of at least two steps.
To solve the problems, further, in the invention, a gel or solid comprising an ion or its derivative including an organic cationic structure containing quaternary nitrogen expressed in formulas (I) to (VI), and different cations at least as coexistent ions is used as an ion conductor, and by composing an electrochemical element by using it, a nonaqueous secondary battery of high energy density or electrochemical element is realized. 
(R1 and R2 are groups having an aliphatic carbon directly bonded to a nitrogen atom.) 
(R3 is an aromatic group, and R4, R5, R6 are groups having an aliphatic carbon directly bonded to a nitrogen atom.) 
(R8 and R9 are groups having an aliphatic carbon directly bonded to a nitrogen atom, and R10 is a group containing at least aliphatic carbon.) 
(R14, R15, R16 and R17 are groups having an aliphatic carbon directly bonded to a nitrogen atom, and at least one of R11, R12 and R13 is an aromatic group, and non-aromatic groups are groups containing carbon) 
(R18 is a group containing at least aliphatic carbon.) 
(R21 and R22 are groups having an aliphatic carbon directly bonded to a nitrogen atom.)
It is a feature of the lithium secondary battery of the invention that its current collector is composed of a specific graphite sheet. More specifically, it is manufactured by baking high polymer film, and a flexible graphite sheet capable of folding at radius of curvature of 1 mm or less and angle of 160 degrees or more is used as the current collector.
As a result, as compared with the conventional battery using the metal current collector of large specific gravity, the battery of the invention is reduced in weight, and the contact with the active material is improved, so that the lithium ion secondary battery having excellent cycle characteristic and high energy density can be presented.
The invention provides a carbon material prepared by adding an aromatic compound of 2 to 10 rings to a high polymer before curing, and heating the cured resin. The cured resin produces fine crystals of carbon called crystallites at the time of carbonization taking place after pyrolysis from 300xc2x0 C. to about 600xc2x0 C. Crystallites occurring in such process produce many defects inside, and large gaps (pores) are formed between adjacent crystallites.
On the other hand, in the cured resin dispersing an aromatic compound of 2 to 10 rings, crystallites are more likely to be generated. Besides, since the aromatic compound has a flatness, defects inside the crystallites decrease, and gaps (pores) between adjacent crystallites are narrower, and pores ( less than 10 xc3x85) in the size contributing to lithium absorption are formed.
As the high polymer before curing, various commercial high polymers may be used, and in particular, preferably, phenol resin, polyamide acid, and furfuryl alcohol resin are used. These high polymers produce isotropic carbons by heat treatment so as to facilitate formation of pores.
Of these high polymers, in particular, by using a phenol resin using methyl phenol or dimethyl phenol as the base, fine pores are formed more easily.
On the other hand, as the additive, the aromatic compound is not preferred to be linear if having 3 or more rings. If linear, the flatness of crystallites formed after carbonization becomes poorer than in non-linear composition, and the formed pores are larger than the size for absorbing lithium.
As a method of controlling the structure of crystallites, it is preferred that the cured resin is pulverized beforehand. If pulverized after carbonization, mechanical force is applied to the carbon structure, and the formed pore structure may be disturbed.
Heat treatment of the cured resin for controlling the structure of crystallites is preferred to be done in inert atmosphere or in vacuum. In the case of inert atmosphere, the concentration of the substance for giving activation effect to carbon, for example, oxygen or carbon dioxide, must be 100 ppm or less. If such substances are contained by more than 100 ppm, the carbon receives activation from the surface, and the pores as reaction sites of lithium are destroyed.
The heat treatment temperature of the cured resin is 800xc2x0 C. or more and 1400xc2x0 C. or less, and preferably 900xc2x0 C. or more and 1200xc2x0 C. or less. If less than 800xc2x0 C., although the capacity is large, the discharge curve has a plateau at +0.8 V for the equilibrium potential of lithium. In such discharge curve, the potential of the battery cannot be heightened, and it is not preferred. At heat treatment over 1400xc2x0 C., crystallites are grown, pores are destroyed, and the discharge capacity is lowered.
Further, to raise the capacity, an aromatic compound of 2 to 10 rings is added to the high polymer before curing, and the cured resin is heated after reaction of aromatic compound and high polymer. As the high polymer before curing, any polymer inducing crosslinking reaction may be used, and phenol resin, polyamide acid, and furfuryl alcohol resin are preferably used.
For the ease of crosslinking reaction between the high polymer and aromatic compound, it is preferred that the aromatic compound may contain at least one phenolic hydroxyl group. As a result, the electron state of the aromatic high polymer is varied, and the adjacent portion of the phenolic hydroxyl group becomes active.
The aromatic compound used at this time is not preferred to be linear if having 3 or more rings. If the aromatic compound is linear, the flatness of crystallites formed after carbonization becomes poorer than in branched composition, and the formed pores are larger than the size for absorbing lithium.
The cured resin thus obtained is usually solid, and it may be used directly, but is preferred to be used as powder.
Such cured resin is heated in inert atmosphere or vacuum at 800xc2x0 C. or more to 1400xc2x0 C. or less. By dividing this heat treatment process in at least two steps, the characteristics may be further enhanced.
The first step of heat treatment is a process necessary for removing the gas generated at the time of heat treatment sufficiently at low temperature. The gas generated at the time of heat treatment gives activation effect to the carbon, and multiple functional groups containing oxygen are formed on the carbon surface.
Such carbon increases the irreversible capacity which is the difference between the initial charge capacity and the initial discharge capacity, and it is inappropriate as negative electrode material. This heat treatment temperature must be 700xc2x0 C. or less. After this heat treatment process, heat treatment at 800xc2x0 C. or more to 1400xc2x0 C. or less may be done either consecutively or after once cooling.
Incidentally, the heat treatment at 700xc2x0 C. or less may be followed by pulverization. After this heat treatment, since the cured resin is promoted in carbonization, pulverization may be done efficiently.
It is a feature of the invention to heat the cured resin. For this heat treatment, usually, an annular furnace may be used, but it is preferred to use an inducting heating furnace. In the annular furnace, the heat invades inside through the surface, first the surface is carbonized, and the carbonization gradually advances inside.
As a result, the surface comes to have a structure less likely to allow gas transmission, and the gas generated by pyrolysis in the inside is not removed smoothly, and the degree of carbonization differs between the surface and the inside. Accordingly, the action as the electrode mainly takes place on the surface, and the action of the inside of the carbon as the electrode is small, and it is not desired. To avoid this, the entire structure must be uniformly carbonized.
It is realized by using an induction heating furnace for heat treatment of the cured resin.
Thus obtained carbon material may be used as the negative electrode material of nonaqueous electrolyte secondary battery.
The invention relates to an electrochemical element comprising a gel or solid ion conductor using an ion or its derivative including a structure shown in formula (I), and different cations at least as coexistent ions and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
The invention also relates to an electrochemical element comprising a gel or solid ion conductor using an ion or its derivative including a structure shown in formula (II), and different cations at least as coexistent ions and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
The invention further relates to a gel or solid ion conductor comprising an ion or its derivative including a structure shown in formula (III), and different cations at least as coexistent ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
The invention further relates to a gel or solid ion conductor comprising an ion or its derivative including a structure shown in formula (IV), and different cations at least as coexistent ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
The invention further relates to a gel or solid ion conductor comprising an ion or its derivative including a structure shown in formula (V), and different cations at least as coexistent ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
The invention further relates to a gel or solid ion conductor comprising an ion or its derivative including a structure shown in formula (VI), and different cations at least as coexistent ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, a metal lithium electrode.
In the invention, the number of carbon atoms of R10 in (III), the number of carbon atoms of R13 in (IV), and the number of carbon atoms of R18 in (V) are 1 or more to 16 or less, and the ion conductor is characterized by containing at least one of alkyl group, aromatic group, group containing ether bond, group containing carbonyl group, nitrile cyano group, and alcohol hydroxyl group, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention relates to a gel or solid ion conductor comprising an ion having two or more structures selected from (I) to (VI) or structures derived therefrom within same ions, and different cations at least as coexistent ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an ion conductor of which coexistent cations contain at least metal ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an ion conductor of which metal ions contain at least one selected from alkaline metal, alkaline earth metal, silver ion, copper ion, and zinc ion, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an ion conductor of which coexistent cations contain at least straight chain alkyl quaternary ammonium ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an ion conductor of which straight chain alkyl group in each one of quaternary ammonium ions has 1 to 4 carbon atoms, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an electrochemical element of which coexistent cations contain at least metal ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an electrochemical element of which metal ions contain at least one selected from alkaline metal, alkaline earth metal, silver ion, copper ion, and zinc ion, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an electrochemical element of which coexistent cations contain at least straight chain alkyl quaternary ammonium ions, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention further relates to an electrochemical element of which each one of straight chain alkyl groups in quaternary ammonium ions has 1 to 4 carbon atoms, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
Moreover, the invention relates to an electrochemical element characterized by using an ion conductor, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention also relates to an electrochemical element capable of storing or supplying electric energy, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
The invention also relates to an electrochemical element capable of storing or supplying electric energy by oxidation and reduction reaction, and by using it, the capacity of the nonaqueous secondary battery can be increased by using, for example, metal lithium electrode.
In the foregoing aspects, the nonaqueous secondary battery is presented as an example, but the invention not specified as the nonaqueous secondary battery in the claims is not limited to the nonaqueous secondary battery alone, but may be applied to condenser and other electrochemical elements.
The invention uses an ion conductor of gel or solid form, and as far as the ion conduction function is utilized for operating the electrochemical element, the element is not necessarily required to store or supply the electric energy.
The invention presents a nonaqueous secondary battery having a positive electrode and a negative electrode for absorbing and releasing lithium ions, and using an ion conductor containing lithium ions as electrolyte, and more specifically a nonaqueous secondary battery using a positive electrode and a negative electrode in which the structure of the crystal lattice and the array of lithium ions to be absorbed are in a mismatched relation when absorbing and releasing lithium ions, and as compared with the conventional positive active material, the discharge capacity is large, and the flat area of potential is very wide. In the embodiment, the nonaqueous secondary battery is shown as an example, but the invention not specified as the nonaqueous secondary battery in the claims is not limited to the nonaqueous secondary battery alone, but may be applied to condenser and other electrochemical elements. That is, the invention relates to an electrochemical element comprising a gel or solid ion conductor containing a nonionic high polymer, an ion or its derivative including a structure shown in (I), and different cations at least as a coexistent ion, and by using it, a higher energy density of electrochemical element is realized.
The invention relates to an electrochemical element of which ion conductor is gel at room temperature, and by using it, a higher energy density of electrochemical element is realized.
The invention also relates to an electrochemical element of which coexistent cations contain at least a metal ion, and by using it, a higher energy density of electrochemical element is realized.
The invention further relates to an electrochemical element of which metal ions contain at least lithium ions in particular, and by using it, a higher energy density of electrochemical element is realized.
The invention further relates to an electrochemical element of which coexistent cations contain at least quaternary ammonium ions, and by using it, a higher energy density of electrochemical element is realized.
The invention further relates to an electrochemical element of which quaternary ammonium ions contain at least straight chain alkyl quaternary ammonium ions, and by using it, a higher energy density of electrochemical element is realized.
The invention provides a nonaqueous secondary battery having an electrode for absorbing and releasing lithium ions, and by using it, a higher energy density of electrochemical element is realized.
The invention presents a lithium ion secondary battery characterized by using a flexible graphite sheet as a current collector, and as compared with the conventional metal collector of copper or nickel, the weight is lighter, and the battery weight can be reduced by using the current collector of the invention, so that the energy density per unit weight of the battery is enhanced. Moreover, since the current collector of the invention is flexible, the shape of the battery is not limited to square or cylindrical type alone, but it is applicable to batteries of various shapes such as sheet, square, cylindrical and other types.
By using the current collector of the invention in the large-sized power source for electric vehicle or the like, its weight is reduced, and the energy density per unit weight is increased, and the driving distance by one charge is notably extended.
Moreover, since the contact between the active material and the current collector of the invention is excellent, preventing decrease of electric capacity due to drop of contact between the current collector and active material due to charging and discharging cycles, a lithium ion secondary battery excellent in cycle characteristics can be presented.
The invention presents a lithium ion secondary battery of which graphite sheet is manufactured by baking an aromatic polyimide film of film thickness of 300 xcexcm or less in an inert gas at maximum temperature of 2500xc2x0 C. or more, and the graphite sheet of high quality and excellent flexibility is manufactured, and by using it as the current collector, the lithium ion secondary battery of light weight and large energy density per unit weight is presented.
In the lithium ion secondary battery of the invention, the electric conductivity of the graphite sheet is in a range of 2500 S/cm or more to 5500 S/cm or less, so that a lithium ion secondary battery of light weight, excellent cycle characteristics, and large capacity is presented.
In the lithium ion secondary battery of the invention, the graphite sheet density is in a range of 0.4 g/cc to 1.5 g/cc, so that a lithium ion secondary battery of light weight, excellent cycle characteristics, and large capacity is presented.
In the lithium ion secondary battery of the invention, the structure of the graphite sheet is characterized by that the plane interval of (002) planes of the graphite is in a range of 0.3354 nm to 0.3375 nm. By using the graphite sheet having such structure as the current collector, the battery weight can be reduced, and the energy density per unit weight of the battery is increased. Moreover, since the current collector of the invention is flexible, the shape of the battery is not limited, and it is applied to batteries of various shapes including sheet, square, cylindrical and others.
By using the current collector of the invention in the large-sized power source for electric vehicle or the like, its weight is reduced, and the energy density per unit weight is increased, and the driving distance by one charge is notably extended.
Moreover, since the contact between the active material and the current collector of the invention is excellent, preventing decrease of electric capacity due to drop of contact between the current collector and active material due to charging and discharging cycles, a lithium ion secondary battery excellent in cycle characteristics can be presented.
The invention presents a lithium ion secondary battery in which either one of amorphous carbon and graphite or a mixture thereof is provided on the graphite sheet as negative active material, and therefore since the weight is lighter as compared with the metal current collector of copper or nickel used in the conventional current collector, the battery weight can be reduced by using the current collector of the invention, so that the energy density per unit weight of the battery can be increased.
The current collector of the invention has, aside from the current collecting function, a function of absorbing and releasing lithium, thereby having an action of presenting a lithium ion secondary battery of high energy density substantially increased in the amount of the active material. Similarly, by using the current collector of the invention in the large-sized power source for electric vehicle or the like, its weight is reduced, and the energy density per unit weight is increased, and the driving distance by one charge is notably extended.
Moreover, since the contact between the active material such as amorphous carbon or graphite carbon and the current collector of the invention is excellent, preventing decrease of charge and discharge capacity due to drop of contact between the current collector and active material due to charging and discharging cycles, a lithium ion secondary battery excellent in cycle characteristics can be presented. Moreover, since the current collector of the invention is flexible, the shape of the battery is not limited, and it is applied to batteries of various shapes including sheet, square, cylindrical and others.
In the lithium ion secondary battery of the invention, at least one side of the graphite sheet is preliminarily treated to be multiporous by physical or mechanical method, and then the negative active material is provided, so that, by such surface treatments, the current collector of the invention is improved in, aside from the current collecting function, the function as the negative active material for absorbing and releasing lithium by itself, as compared with untreated current collector.
Therefore, by providing the negative active material after surface treatment of the invention, a lithium ion secondary battery of light weight and large capacity is presented.
Moreover, in the lithium ion secondary battery of the invention, after multiporous treatment of at least one side of the graphite sheet preliminarily by laser irradiation, either amorphous carbon or graphite carbon, or a mixture thereof is provided as a negative active material, and therefore, by this surface treatment, the current collector of the invention is improved in, aside from the current collecting function, the function as the negative active material for absorbing and releasing lithium by itself, as compared with untreated current collector.
Hence, by providing the negative active material after surface treatment of the invention, a lithium ion secondary battery of light weight and large capacity is presented.
The invention further presents a lithium ion secondary battery characterized by using a composition of either amorphous carbon or graphite carbon, or their mixture disposed on the graphite sheet as negative active material, so that a lithium ion secondary battery of light weight, excellent cycle characteristics and large capacity can be presented.
The invention further presents a lithium ion secondary battery characterized by using as an active material layer, an amorphous carbon, which is synthesized on a graphite sheet by heat-treating phenol resin in a temperature range of 700xc2x0 C. to 1500xc2x0 C., so that a lithium ion secondary battery of light weight and large capacity can be presented.
The invention further presents a lithium ion secondary battery characterized by disposing spherical, acicular or scaly graphite or mixture thereof on a graphite sheet, so that a lithium ion secondary battery of light weight and large capacity can be presented.
Further, in the lithium ion secondary battery of the invention, more specifically, the carbon powder on the graphite sheet has a mean particle size of 15 xcexcm or less, and the thickness of the carbon powder layer is in a range of 0.05 mm to 0.3 mm, and the bulk density is in a range of 0.7 g/cc to 1.5 g/cc, so that a lithium ion secondary battery of light weight and large capacity can be presented.
The invention also presents a lithium ion secondary battery characterized by disposing an active material in powder form on a graphite sheet by printing method from paste state, so that a lithium ion secondary battery of light weight and large capacity, excellent in productivity, can be presented.
The invention also presents a lithium ion secondary battery characterized by disposing one of lithium cobaltate, lithium nickelate and lithium manganate, or a mixture thereof on a graphite sheet as a positive active material, so that a lithium ion secondary battery of light weight and increased energy density per unit weight can be presented.
The invention also presents a lithium ion secondary battery characterized by utilizing one or both of compositions having a positive active material or negative active material disposed on a graphite sheet as the electrode of the secondary battery for automobile, and since the weight is lighter as compared with the metal current collector of copper or nickel used in the conventional current collector, by using the current collector of the invention, the battery weight can be reduced, the energy density per unit weight of the battery is increased, and when used in the large-sized power source for automobile, its weight is reduced, and the energy density per unit weight is increased, and the driving distance by one charge is notably extended.
In the battery of the invention, various materials used in the conventional lithium ion secondary battery can be used in combination, and are not particularly limited.
For example, as the negative active material of the battery of the invention, carbonaceous materials capable of absorbing and releasing lithium can be used. Such materials include graphite, baked and carbonized materials of high polymer compound (phenol resin, furan resin), glass carbons, carbon fibers, activated carbon and others.
The positive active material includes compounds containing lithium capable of charging and discharging. For example, it is expressed in a general formula LixMOy (M means transition metal element such as Co, Ni, Mn and Fe, x is 0xe2x89xa6xxe2x89xa62, and y is 1xe2x89xa6yxe2x89xa65), and specific examples include LiCoO2, LiNiO2, LiMnO2, and LiMn2O2. It is also effective to use any one of AV4O11, AxV4-zMzO11, AxByV4-zMzO11 (A, B, and M are metal elements, and x, y and z are 0 or more to 4 or less), or their mixture.
As organic solvent of nonaqueous electrolyte solution, propylene carbonate, ethylene carbonate, 1,2-butylene carbonate, 1,2-dimethoxy ethane, xcex3-butyrolactone, tetrahydrofuran, 2-methyl tetrahydrofuran, dioxane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and dipropyl carbonate may be used either alone or in a mixture of two or more kinds.
Examples of supporting electrolyte include LiPF6, LiClO4, LiAsF6, LiSbF6, LiBF4, LiI, LiBr, LiCl, LiSO3CH3, LiSO3CF3, and others.
The nonaqueous electrolyte used in the battery of the invention is not limited to liquid, but may be in gel or solid form.
The thickness, shape, and aperture rate of the current collector of the invention may be optimized depending on the kind of the active materials of the positive electrode and negative electrode of the battery, kind of electrolyte solution or electrolyte, or purpose of use of battery.
Thus, according to the invention, for realizing the nonaqueous secondary battery of high energy density and high repeating stability, constituent elements and the nonaqueous secondary battery using the same are obtained.
Further, by using a gel or solid ion conductor containing a nonionic high polymer, an ion including the structure shown in (I) or its derivative, and different cations at least as coexistent ions, an electrochemical element is obtained, so that a higher energy density is realized.
Since the conventional metal current collector is not used in the invention, the battery weight can be reduced. Further, the current collector of the invention has a function of working as active material by itself, aside from the current collecting function, so that a higher capacity is obtained.
Thus, according to the secondary battery using the current collector of the invention, a novel secondary battery of light weight and high energy density is presented, and it is expected to be particularly effective in large-sized structure such as the power source for an electric vehicle.
Moreover, the contact between the active material and the current collector of the invention is excellent, and it prevents decrease of battery capacity due to drop of contact between the current collector and active material due to charging and discharging cycles, so that a battery excellent in cycle characteristics may be presented.